Inhibitory Effects Of Polyphenols Research Articles

Inhibitory effects of polyphenols on the Maillard reaction in low-lactose milk and the underlying mechanism

In this study, low lactose milk (LLM) was heat-treated under different conditions and stored at 4, 25 and 37°C for 15 d, after which the changes in the Maillard reaction (MR) of LLM were investigated. The contents of α-dicarbonyl compounds and 5-hydroxymethylfurfural(5-HMF) in LLM after the addition of polyphenols were determined via HPLC, and the inhibitory effects of 3 different concentrations of epigallocatechin gallate (EGCG), dihydromyricetin (DMY), and procyanidin (PC) on the MR of LLM were studied. The fluorescence intensity of LLM was measured at 290, 300 and 310 K, the fluorescence quenching types and binding constants of PC on casein were investigated, and thermodynamic analysis was carried out. These results suggest that the optimal heat treatment conditions were 80°C for 15 s and that the optimal storage conditions were 4°C. In the α-dicarbonyl compound capture and 5-HMF inhibition tests, PC had the greatest inhibitory effect at a concentration of 0.2 mg/mL, with an inhibition rate of 48.19%. Therefore, PC is more stable than the other 2 polyphenols. The mechanism of inhibition involves the formation of matrix complexes between PC and casein in LLM, resulting in static quenching of the LLM and thus a reduction of the inhibitory effect. The thermodynamic analysis revealed that the binding of PC to casein was an exothermic reaction, and the combination of the 2 was driven mainly by hydrogen bonding and van der Waals forces. This study lays a theoretical foundation for the development of LLM.

A review of the therapeutic effects of polyphenols on non-alcoholic fatty liver disease: Focus on oxidative stress

A substantial body of research suggests that polyphenols may have health benefits, particularly in metabolic disorders associated with obesity, such as non-alcoholic fatty liver (NAFLD), type 2 diabetes, and cardiovascular disease. Given the importance of oxidative stress in the pathogenesis of metabolic disorders, significant emphasis has recently been placed on the characteristics of polyphenols in obesity-related problems. This narrative review summarizes the current knowledge on the inhibitory effects of polyphenols, including curcumin, resveratrol, baicalin, nobiletin, and quercetin, on oxidative stress, with a focus on the role of the Nrf2 pathway. This review compiles the data from articles showing that the aforementioned polyphenols improve health in metabolic diseases by regulating Nrf2 and its target proteins involved in reducing oxidative stress. However, due to the limitations of in vitro and in vivo investigations, as well as the lack of long-term human clinical trial studies, further high-quality research is required to definitively demonstrate the clinical usefulness of polyphenols for the prevention and management of NAFLD.

Inhibitory effect of polyphenols from sumac, pomegranate and Indian almond on urease producing bacteria and jack bean urease activity

Urinary tract infection caused by Klebsiella, Proteus and Streptococcus is a urease dependent process, hence treatment of these infections by antibacterial compounds lies in inhibition of their virulence factors. The crude methanolic extracts derived from sumac fruit, pomegranate peel and Indian almond leaves were separated into anthocyanin and non-anthocyanin fractions using solid phase cartridges. The inhibitory effect of these fractions was determined on the growth of urease producing species and jack bean urease activity. Known compounds in the fractions were also docked with ureases of different biological origins viz. K. pneumoniae (PDB ID: 8HCN), K. aerogenes (PDB ID: 2KAU), Helicobacter pylori (PDB ID:8HC1)and Canavalia ensiformis (jack bean) (PDB ID: 3LA4) to determine their binding affinities and interaction with the enzyme. All the fractions showed significant inhibition growth for P. mirabilis, S. epidermidis and K.pneumoniae. Among the samples, sumac showed greatest inhibition against all (MIC 6-25 mg.mL−1) while among the fractions, anthocyanin was found to be most active (MIC 6-12 mg/mL). Likewise, all fractions inhibited urease with lowest ICs50 shown by sumac fractions (21-116 μg.mL−1). Out of 39 compounds docked, 27 showed interaction with movable flaps and/or active site of ureases which explains their mode of inhibition.

Evaluating the potential of Hibiscus sabdariffa beverage to address the prevalence of iron deficiency in sub-Saharan Africa

The potential of Hibiscus sabdariffa L. beverage as a dietary iron source for sub-Saharan Africans was investigated. The target was to provide 6 mg of iron through 250 mL of the beverage daily. However, the iron content of the dried hibiscus calyces was determined to be 9.73 ± 0.31 mg/100 g and from that only ∼30% was extractable, resulting in 0.93 ± 0.19 mg Fe/250 mL of the selected beverage formulation. Therefore, ferrous sulfate was explored as a fortificant. The beverage contains polyphenols which could form non-absorbable chelation complexes with iron during digestion. Subsequently, the effect of polyphenols on the bioaccessibility of native and added iron was assessed using spectrophotometric methods. The presence of iron-polyphenol complexes in samples of the unfortified and fortified beverages, adjusted to pH 6.5 (pH at site of iron absorption in the gut) was established. However, only ∼25% of the added iron was found to be bound in the complex. It was shown that the viability of H. sabdariffa L. beverage as an iron source is impacted by extraction losses and the inhibitory effect of polyphenols. Nonetheless, if iron-polyphenol complexation was reduced/prevented then, a fortified hibiscus beverage could be a useful iron source.

The starch-polyphenol inclusion complex: Preparation, characterization and digestion

Debranched rice starch and different polyphenols, including genistein, quercetin, naringin, gallic acid, ferulic acid and caffeic acid, formed the V-type inclusion complex, which was confirmed by diffraction peaks at 7.5°, 13.0° and 20.0° and the presence of the endothermic peak during DSC analysis. Moreover, the inhibitory effect of polyphenols on α-amylase was in the order of quercetin > genistein > gallic acid = ferulic acid > naringin = caffeic acid, and their inhibitory effect on amyloglucosidase was in the order of quercetin = naringin > gallic acid > caffeic acid = genistein > ferulic acid. The starch-genistein and starch-naringin complexes had the highest polyphenol content, followed by the starch-ferulic acid complex, the starch-caffeic acid complex, the starch-quercetin complex and the starch-gallic acid complex. The resistant starch content of starch-genistein, starch-quercetin, starch-naringin, starch-gallic acid, starch-ferulic acid and starch-caffeic acid complexes was 72.49%, 79.86%, 68.82%, 60.96%, 71.06% and 71.24%, respectively. These results suggested that these starch-polyphenol inclusion complexes were highly resistant to digestion. Particularly, the starch-quercetin complex was the most resistant, which might be due to that its highest crystallinity and the strongest inhibitory effect of quercetin on amylases.

Inhibitory effects of polyphenols from black chokeberry on advanced glycation end-products (AGEs) formation

Plant-based polyphenols are known to exert mitigating effects on the harmful consequences of advanced glycation. In this study, the antioxidant and antiglycation properties of purified black chokeberry polyphenol and its dominant monomers were studied. The phenolics of black chokeberry had a significant inhibitory effect on glycation products at all stages. The highest inhibition of fructosamine (72.27%) was achieved by chlorogenic acid (CA). Epigallocatechin gallate (EGCG) showed an 84.47% inhibition of α-dicarbonyl and 54.44% inhibition of AGEs (advanced glycation end-products). However, the inhibition of α-dicarbonyl was impacted by the presence of Cu2+. In addition, an EGCG-induced increase in the protein α-helical structure to 21.43% was observed. Overall, EGCG was the main component inhibited protein glycosylation in the simulated glycation system. Furthermore, the mechanism of inhibition was a combination of scavenging free radicals, capturing metal ions, and alleviating changes in the secondary structure of proteins.

Inhibitory Effect of Polyphenols from the Whole Green Jackfruit Flour against α-Glucosidase, α-Amylase, Aldose Reductase and Glycation at Multiple Stages and Their Interaction: Inhibition Kinetics and Molecular Simulations.

For the first time, α-glucosidase, α-amylase, aldose reductase, and glycation at multiple stages inhibitory assays were used to explore the antidiabetic potential of whole unripe jackfruit (peel with pulp, flake, and seed). Two polyphenols (phenolic acids) with strong antihyperglycaemic activity were isolated from the methanol extract of whole jackfruit flour (MJ) using activity-guided repeated fractionation on a silica gel column chromatography. The bioactive compounds isolated were identified as 3-(3,4-Dihydroxyphenyl)-2-propenoic acid (caffeic acid: CA) and 4-Hydroxy-3,5-dimethoxybenzoic acid (syringic acid: SA) after various physicochemical and spectroscopic investigations. CA (IC50: 8.0 and 26.90 µg/mL) and SA (IC50: 7.5 and 25.25 µg/mL) were identified to inhibit α-glucosidase and α-amylase in a competitive manner with low Ki values. In vitro glycation experiments further revealed that MJ and its components inhibited each stage of protein glycation as well as the generation of intermediate chemicals. Furthermore, CA (IC50: 3.10) and SA (IC50: 3.0 µg/mL) inhibited aldose reductase effectively in a non-competitive manner, respectively. The binding affinity of these substances towards the enzymes examined has been proposed by molecular docking and molecular dynamics simulation studies, which may explain their inhibitory activities. The found potential of MJ in antihyperglycaemic activity via inhibition of α-glucosidase and in antidiabetic action via inhibition of the polyol pathway and protein glycation is more likely to be related to the presence of the phenolic compounds, according to our findings.

Inhibitory effect of polyphenols (phenolic acids, lignans, and stilbenes) on cancer by regulating signal transduction pathways: a review.

Natural products, especially polyphenols (phenolic acids, lignans, and stilbenes) are suggested to be more potent anticancer drugs because of their no or less adverse effects, excess availability, high accuracy, and secure mode of action. In the present review, potential anticancer mechanisms of action of some polyphenols including phenolic acids, lignans, and stilbenes are discussed based on clinical, epidemiological, in vivo, and in vitrostudies. The emerging evidence revealed that phenolic acids, lignans, and stilbenes induced apoptosis in the treatment of breast (MCF-7), colon (Caco-2), lung (SKLU-1), prostate (DU-145 and LNCaP), hepatocellular (hepG-2), and cervical (A-431) cancer cells, cell cycle arrest (S/G2/M/G1-phases) in gastric (MKN-45 and MKN-74), colorectal (HCT-116), bladder (T-24 and 5637), oral (H-400), leukemic (HL-60 and MOLT-4) and colon (Caco-2) cancer cells, and inhibit cell proliferation against the prostate (PC-3), liver (LI-90), breast (T47D and MDA-MB-231), colon (HT-29 and Caco-2), cervical (HTB-35), and MIC-1 cancer cells through caspase-3, MAPK, AMPK, Akt, NF-κB, Wnt, CD95, and SIRT1 pathways. Based on accumulated data, we suggested that polyphenols could be considered as a viable therapeutic option in the treatment of cancer cells in the near future.

Inhibitory effects of polyphenols and their colonic metabolites on CYP2D6 enzyme using two different substrates

Polyphenolic compounds (including flavonoids, chalcones, phenolic acids, and furanocoumarins) represent a common part of our diet, but are also the active ingredients of several dietary supplements and/or medications. These compounds undergo extensive metabolism by human biotransformation enzymes and the microbial flora of the colon. CYP2D6 enzyme metabolizes approximately 25% of the drugs, some of which has narrow therapeutic window. Therefore, its inhibition can lead to the development of pharmacokinetic interactions and the disruption of drug therapy. In this study, the inhibitory effects of 17 plant-derived compounds and 19 colonic flavonoid metabolites on CYP2D6 were examined, employing two assays with different test substrates. The O-demethylation of dextromethorphan was tested employing CypExpress 2D6 kit coupled to HPLC analysis; while the O-demethylation of another CYP2D6 specific substrate (AMMC) was investigated in a plate reader assay with BioVision Fluorometric CYP2D6 kit. Interestingly, some compounds (e.g., bergamottin) inhibited both dextromethorphan and AMMC demethylation; however, certain substances proved to be inhibitors only in one of the assays applied. Our results demonstrate that some polyphenols and colonic metabolites are inhibitors of CYP2D6-catalyzed reactions. Nevertheless, the inhibitory effects showed strong substrate dependence.

Polyphenols as Possible Agents for Pancreatic Diseases.

Pancreatic cancer (PC) is very aggressive and it is estimated that it kills nearly 50% of patients within the first six months. The lack of symptoms specific to this disease prevents early diagnosis and treatment. Today, gemcitabine alone or in combination with other cytostatic agents such as cisplatin (Cis), 5-fluorouracil (5-FU), irinotecan, capecitabine, or oxaliplatin (Oxa) is used in conventional therapy. Outgoing literature provides data on the use of polyphenols, biologically active compounds, in the treatment of pancreatic cancer and the prevention of acute pancreatitis. Therefore, the first part of this review gives a brief overview of the state of pancreatic disease as well as the procedures for its treatment. The second part provides a detailed overview of the research regarding the anticancer effects of both pure polyphenols and their plant extracts. The results regarding the antiproliferative, antimetastatic, as well as inhibitory effects of polyphenols against PC cell lines as well as the prevention of acute pancreatitis are presented in detail. Finally, particular emphasis is given to the polyphenolic profiles of apples, berries, cherries, sour cherries, and grapes, given the fact that these fruits are rich in polyphenols and anthocyanins. Polyphenolic profiles, the content of individual polyphenols, and their relationships are discussed. Based on this, significant data can be obtained regarding the amount of fruit that should be consumed daily to achieve a therapeutic effect.

The Effect of Polyphenols on Hypercholesterolemia through Inhibiting the Transport and Expression of Niemann-Pick C1-Like 1.

The Niemann–Pick C1-like 1 (NPC1L1) protein is a cholesterol transporter that is expressed in the small intestine. This report describes the discovery of NPC1L1, its transport properties, and the inhibitory effects of polyphenols on NPC1L1. NPC1L1 was identified in 2004 while searching for ezetimibe molecular targets. Excessive synthesis of cholesterol results in hyperlipidemia, which increases the amount of bile cholesterol excreted into the duodenum. The inhibition of NPC1L1 decreases blood cholesterol because food and bile cholesterol are also absorbed from NPC1L1 in the intestine. Some polyphenols, particularly luteolin, have been reported as NPC1L1-mediated anti-dyslipidemia constituents. Luteolin affects NPC1L1 through two mechanisms. Luteolin directly inhibits NPC1L1 by binding to it, which occurs in a short timeframe similar to that for ezetimibe. The other mechanism is the inhibition of NPC1L1 expression. Luteolin reduced the binding of Sterol-regulatory element-binding protein 2 (SREBP2) in the promoter region of the NPC1L1 gene and decreased mRNA levels of SREBP2 and hepatocyte nuclear factor 4α. These data suggest that luteolin decreases the expression of NPC1L1 through regulation of transcription factors. This review also explores the effect of other polyphenols on NPC1L1 and hypercholesterolemia.

Inhibitory Effect of Epigallocatechin Gallate, Epigallocatechin, and Gallic Acid on the Formation of N-Nitrosodiethylamine In Vitro.

This study investigated the inhibitory effect of epigallocatechin gallate (EGCG), epigallocatechin (EGC), and gallic acid (GA) on the formation of N-nitrosodiethylamine (NDEA) in vitro. Results show that the three polyphenols are capable to block NDEA formation when the molar ratio of phenols to nitrite is higher than 0.8, and a more acidic environment is prone to promote the inhibitory potential of phenols. It is also found that the inhibitory effect tends to decrease in the order: EGCG, EGC, GA, which is in accordance with the order of their DPPH scavenging activity, suggesting that the inhibitory effect of polyphenols on NDEA formation may work through a free radical way. Kinetic study further revealed the three polyphenols react with nitrite at a much faster rate than diethylamine does (P < 0.05). By scavenging nitrite at a faster rate than the nitrosation of diethylamine, polyphenols at high concentration can significantly block NDEA formation. These observations may promote a possible application of polyphenol compounds to inhibit the formation of nitrosamines in food processing. PRACTICAL APPLICATION: The presence of N-nitrosamines in human diet should be an etiological risk factor for human cancers. This work may provide a useful guideline for phenolic compounds to inhibit the formation of nitrosamines in food processing, such as in the process of curing meats. Polyphenols have been proved to block NDEA formation under normal gastric juice condition, suggesting the intake of polyphenols is a potential way to prevent diseases caused by nitrite.

α-Glucosidase inhibitors: consistency of in silico docking data with in vitro inhibitory data and inhibitory effect prediction of quercetin derivatives

The present study aims to investigate the relationship between in silico experimental data and in vitro inhibitory data of polyphenols against α-glucosidase. The CDOCKER protocol in Discovery Studio was used to dock various polyphenols to the Saccharomyces cerevisiae α-glucosidase crystal structure. -CDOCKER energy values and the energy gap between the highest occupied molecular orbital energy and the lowest unoccupied molecular orbital energy were used to study its consistency with in vitro inhibitory data. The results showed that the correlation trend was trustworthy regardless of the data deviation and low correlation coefficient. Despite slight disagreements with some specific polyphenols, the docking data generally explained the effect of the groups (-OH, glycosyl, galloyl, and caffeoyl). The docking results showed that compound 7, a quercetin derivative, can be recommended as a lead antidiabetic compound, with additional anti-obesity effects. Galloyl and caffeoyl moieties are favorable to develop novel αG inhibitors.

Structural analysis of the inhibitory effects of polyphenols, (+)-hopeaphenol and (-)-isohopeaphenol, on human SIRT1.

Human sirtuin 1 (hSIRT1) is a NAD+ -dependent deacetylase that regulates several cellular processes. Unlike resveratrol, natural polymeric phenolic compounds isolated from Vitaceae are mostly hSIRT1 inhibitors. The resveratrol tetramer, (+)-hopeaphenol ((+)-HP), and its geometric isomer, (-)-isohopeaphenol ((-)-iHP), were tested for inhibitory effects on purified hSIRT1 using a fluorescent derivative of peptide substrate p53-AMC (Fluor de Lys) and a cofactor NAD+ . The Lineweaver-Burk plots indicated that both (+)-HP and (-)-iHP were competitive inhibitors against NAD+ . Computer-assisted modeling of the binding of these molecules with hSIRT1 protein provided the most feasible conformation of the enzyme-inhibitor complex. © 2018 BioFactors, 45(2):253-258, 2019.

A-type EGCG dimer, a new proanthocyanidins dimer from persimmon fruits, interacts with the amino acid residues of Aβ40 which possessed high aggregation-propensity and strongly inhibits its amyloid fibrils formation

A-type EGCG dimer is a new proanthocyanidins dimer from persimmon fruits. In the present study, we firstly examined the effects of EGCG and A-type EGCG dimer on Aβ40-fibrillization, and then the detailed mechanisms behind the inhibitory effects of polyphenols on Aβ40 amyloid fibrils formation were investigated by PICUP assay, ESI-MS, NMR and molecular docking. Our results confirmed that A-type EGCG dimer exhibited stronger inhibitory effect on the formation of Aβ40 amyloid fibrils. We found that A-type EGCG dimer possessed more binding sites on Aβ40 peptide than EGCG. Notably, compared with EGCG, A-type EGCG dimer could interact with more amino acid residues which possessed obvious aggregation-propensity. And our results also suggested that the hydrophobic interaction was the principal driving force to inhibit the formation of Aβ40 amyloid fibrils by A-type EGCG dimer. We believed that our study could provide useful insights for the design of low-molecular weight inhibitors of Aβ aggregation.

Investigation of Mammal Arginase Inhibitory Properties of Natural Ubiquitous Polyphenols by Using an Optimized Colorimetric Microplate Assay.

Polyphenols are plant secondary metabolites which possess many positive effects on human health. Although these beneficial effects could be mediated through an increase in nitric oxide synthase activity, little is known regarding the inhibitory effect of polyphenols on mammal arginase, an enzyme which competes with nitric oxide synthase for their common substrate, L-arginine. The aim of the present study was to determine the potential of a series of polyphenols as mammalian arginase inhibitors and to identify some structure-activity relationships. For this purpose, we first developed a simple and cost-effective in vitro colorimetric microplate method using commercially-available mammal bovine liver arginase (b-ARG 1). Among the ten tested polyphenolic compounds [chlorogenic acid, piceatannol, resveratrol, (-)-epicatechin, taxifolin, quercetin, fisetin, caffeic acid, quinic acid, and kaempferol], cholorogenic acid and piceatannol exhibited the highest inhibitory activities (IC50 = 10.6 and 12.1 µM, respectively) but were however less active as (S)-(2-Boronoethyl)-L-cysteine (IC50 = 3.3 µM), used as reference compound. Enzyme kinetic studies showed that both chlorogenic acid and piceatannol are competitive arginase inhibitors. Structural data identified the importance of the caffeoyl (3,4-dihydroxycinnamoyl)-part and of the catechol function in the inhibitory activity of the tested compounds. These results identified chlorogenic acid and piceatannol as two potential core structures for the design of new arginase inhibitors.

Abstract 4655: Plant polyphenols inhibit cellular 24-hydroxylase (CYP24A1) expression and elevate serum 25-hydroxyvitamin D levels

Abstract 1α,25-dihydroxyvitamin D3 (1,25D) is known to regulate various cellular functions, including cell proliferation and differentiation. Both 1,25D and its precursor, 25-hydroxyvitamin D3 [25(OH)D], are catabolized by 24-hydroxylase encoded by the CYP24A1 gene, which is one of the most responsive vitamin D receptor (VDR) target genes, and a is candidate oncogene frequently overexpressed in various malignancies. Therefore, compounds which can inhibit CYP24A1 expression and/or activity, thereby reducing degradation of vitamin D derivatives, may potentiate their anticancer effects. We have previously shown that the plant polyphenols carnosic acid, curcumin and silibinin synergistically enhance differentiation of acute myeloid leukemia (AML) cells induced by near physiologic concentrations of 1,25D. This was associated with the transcription factor Nrf2-assisted elevation of both VDR and the retinoid X receptor alpha (RXRα) protein levels. Here, we demonstrate that despite the latter effect the polyphenols markedly inhibited 1,25D-induced CYP24A1 mRNA expression in AML cell lines but not in osteoblast-like cells. Furthermore, while potentiating 1,25D-induced transactivation of the direct repeat-3 (DR3)-type consensus vitamin D response element (VDRE) in AML cells, as measured by the luciferase (Luc) reporter gene assay, the polyphenols strongly inhibited 1,25D-dependent activation of the CYP24-Luc reporter construct containing an early (-298 bp) promoter region with two critical DR3-type VDREs (VDRE1 and VDRE2). In contrast, the polyphenols failed to inhibit and even enhanced 1,25D-induced transactivation of CYP24-Luc transfected into osteoblastic cells. Inactivating mutations of the VDRE1 or VDRE2 sequence in this construct did not abolish the inhibitory effect of polyphenols. However, overexpression of Nrf2 resulted in reduced CYP24-Luc activation by 1,25D, while dominant-negative Nrf2 had an opposite effect. Importantly, feeding of healthy Balb/c mice with standard rodent chow supplemented with carnosic acid-rich rosemary extract resulted in a marked dose- and time-dependent increase in serum levels of 25(OH)D, as compared to control animals. This was associated with a significant decrease in CYP24A1 mRNA levels in the kidneys of these mice. Collectively, the above data suggest that by downregulating CYP24A1 in a tissue-dependent manner, plant polyphenols may potentiate therapeutic and preventive effects of vitamin D derivatives. These findings may also contribute to our understanding of the beneficial effects of healthy diets. (Supported by the Israel Science Foundation grant 635/11 to M.D. and Y.S. and by the American Institute for Cancer Research grant #10A049 to G.P.S. and M.D.). Citation Format: Ehud Sharony, Ze'ev Barvish, Victoria Novik, Marina Khanin, Merav Cohen-Lahav, Doron Amichay, Yoav Sharoni, George P. Studzinski, Michael Danilenko. Plant polyphenols inhibit cellular 24-hydroxylase (CYP24A1) expression and elevate serum 25-hydroxyvitamin D levels. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4655. doi:10.1158/1538-7445.AM2015-4655

Inhibitory effects of polyphenols from grape pomace extract on collagenase and elastase activity

Breakdown and disorganization of extracellular matrix proteins like collagen, fibronectin and elastin are main characteristics of skin aging due to the enhanced activation of proteolytic enzymes such as collagenases and elastases. Inhibition of their enzymatic activities by natural plant compounds might be a promising approach to prevent extrinsic skin aging. Especially polyphenols are supposed to interact with those enzymes due to their molecular nature. In our investigation, extracts of pomace from Riesling grapes were analyzed for their inhibitory properties on collagenase as well as elastase. Crude grape pomace extract showed a dose-dependent inhibitory activity against both enzymes with IC50‐values of 20.3μg/ml and 14.7μg/ml for collagenase and elastase activity, respectively. The extracts were fractionated into four fractions containing phenolic compounds differing in chemical structure and polarity. Except for the stilbene containing fraction, all other fractions showed inhibitory effects on both enzyme activities. The most pronounced impact was found for the hydrophilic low molecular weight polyphenols containing the free phenolic acids. In particular, gallic acid showed considerable inhibition values. EGCG was used as a positive control and showed a dose-dependent inhibition of collagenase activity (IC50=0.9mM).

Inhibitory effect of polyphenols in Houttuynia cordata on advanced glycation end-products (AGEs) by trapping methylglyoxal

The inhibitory effect of bioactive components from Houttuynia cordata (H. cordata) on advanced glycation end-products (AGEs) by trapping methylglyoxal (MGO) was investigated. MGO and its adducts of quercitrin, chlorogenic acid, rutin was analyzed by using liquid chromatography-mass spectrometry (LC-MS/MSn). The remaining MGO were 52.3, 26.7, and 9.4% for chlorogenic acid, quercitrin, and rutin, respectively and the mono- or di-MGO conjugated adducts of quercitrin and rutin were identified at 24 h of reaction. The formation of AGEs was detected through the reaction of glucose with protein by the fluorescence method. During the glycation reaction, quercitrin, rutin, and methanol extract of H. cordata decreased the production level of AGEs by 91–94.6 %. H. cordata containing chlorogenic acid, quercitrin, and rutin may have potential role in minimizing AGEs formation.

Inhibitory effects of polyphenols from water chestnut (Trapa japonica) husk on glycolytic enzymes and postprandial blood glucose elevation in mice

Water chestnut is an annual aquatic plant that grows in Asia and Europe. Although water chestnut has been used as food and herbal medicine, its physiological functions and active ingredients are unknown. Here, we extracted polyphenols from the husk of the Japanese water chestnut (Trapa japonica) and assessed their effects on blood glucose levels. Three hydrolysable polyphenolics (WCPs), eugeniin, 1,2,3,6-tetra-O-galloyl-β-d-glucopyranose, and trapain, were predominant with dry-weight contents of 2.3±0.0, 2.7±0.1, and 1.2±0.1g/100g, respectively. These WCPs exhibited inhibitory activity against α-amylase and α-glucosidase. Whereas (−)-epigallocatechin gallate does not inhibit α-amylase, WCPs exhibited high inhibitory activity (>80% at 0.15mg/mL). In mice, administration of WCPs (40mg/kg) significantly reduced blood glucose and serum insulin levels as assessed by the carbohydrate tolerance test.